This disclosure generally relates to a method for repairing articles made of ceramic composites. In particular, the present invention relates to a method for repairing articles made of fiber-reinforced ceramic matrix composites.
Reinforced ceramic matrix composites (“CMCs”) comprising fibers dispersed in continuous ceramic matrices of the same or a different composition are well suited for structural applications because of their toughness, thermal resistance, high-temperature strength, and chemical stability. Such composites typically have high strength-to-weight ratio that renders them attractive in applications in which weight is a concern, such as in aeronautic applications. Their stability at high temperatures renders them very suitable in applications in which the components are in contact with a high-temperature gas, such as in gas turbine engine.
One process for the production of CMCs begins with producing a prepreg tape comprising fibers and a ceramic matrix or matrix precursor material. Fibers, such as ceramic fibers that have been coated with one or more materials to impart certain desired surface properties to them, are impregnated with a suspension comprising powder of the ceramic matrix or matrix precursor material and a temporary binder, and typically wound onto a drum to form the prepreg tape. The prepreg tape is dried and then cut into sections and formed into a fiber preform that is a porous object having a desired shape. The dried prepreg tape is still flexible and can be easily shaped. In another process, the preform is made first using tapes of woven fibers or fibers woven into three-dimensional structures, and fiber coatings are applied by chemical vapor infiltration. The porosity within the fiber preform is then filled with the matrix or matrix precursor material, which in many instances may be a molten metal or metalloid such as silicon, which eventually produces the finished continuous ceramic matrix surrounding the fibers. Silicon carbide fibers have been used as a reinforcing material for ceramic matrices, such as silicon carbide, titanium carbide, silicon nitride, and aluminum oxide. The filling of the fiber preform with the matrix precursor material and any attendant reaction between the matrix constituents already in the preform and the precursor material serve to densify the shaped object. This filling or densification may be achieved by chemical-vapor infiltration (“CVI”) or liquid-phase infiltration by the matrix precursor material. Liquid-phase infiltration, often by a molten metalloid, is the preferred method because it is less time consuming and more often produces a fully dense body than the CVI process. Full densification is typically desired to achieve good thermal and mechanical properties and, thus, a long-term performance of CMCs.
Polymer infiltration and pyrolysis (“PIP”) is another process for the production of CMCs. This process consists of: (1) infiltration of the composite reinforcement preform with one or more organo-metallic polymers, (2) densification or consolidation of the polymer-impregnated reinforcement preform, (3) cure of the polymer matrix to prevent melting during subsequent processing, and (4) pyrolysis and conversion of the cured polymer or polymers into the ceramic matrix. The polymer infiltration of a preform can be accomplished by either solution infiltration or melt infiltration. Ceramic composite matrices, such as silicon carbide, silicon nitride, silicon oxy-nitride, boron nitride, aluminum nitride, and mixtures thereof, can be prepared from the pyrolysis of respective precursor polymers.
CMCs are comparatively more expensive than more conventional materials because their typical production process is rather complicated. Therefore, it would be desirable to have a method for repairing CMC components that may be damaged during processing, handling, or use.